Empty/load valves are well known in the art. See, for example, U.S. Pat. Nos. 4,648,661; 4,826,259; 4,844,554 and 4,824,179. In general, the valve includes a reciprocable rod extending from the valve housing which actuates a changeover valve within the housing and which is actuated by pivotable measuring arm mounted on, but externally of, the valve housing. The position of the arm, and hence, the rod and the braking pressure, is determined by the load on the vehicle. Generally speaking, the length dimension of the arm and the pivot point of the arm are selected so that the length dimension of the arm intersects the axis of said rod.
One of the problems with the prior art devices is that the valves usually are located where they are subject to dust, dirt, other particulates, rust and moisture. Such foreign substances can interfere with the movement of the arm and actuation of said rod and hence, the operation of the valve.
It has been proposed to protect the rod and the arm where it engages the rod by an accordian pleated rubber boot. See, for example, U.S. Pat. No. 4,824,179. While such a boot is reasonably satisfactory when initially installed, it deteriorates relatively rapidly under the conditions of use and develops cracks or becomes torn thereby losing its effectiveness as protection for the arm and the actuating rod.